The present invention relates to a coating composition and, more particularly, to a coating composition which can be prepared in accordance with the sol-gel process and provides a coating film having excellent physical properties when the coating composition is applied to the surface of metal, wood, paper, cloth, glass, ceramics, concrete or a synthetic resin by spray coating and cured at a low temperature in the range of the room temperature to about 200xc2x0 C.
Heretofore, a coating material forming a coating layer having a high hardness and exhibiting excellent weatherability, water resistance, chemical resistance and adhesion at a low cost has been desired and many proposals have been made. As an inorganic coating material, complexes composed of sols of oxides and organosilanes which provide organo-polysiloxanes by hydrolysis and polycondensation have mainly been examined.
For example, in Japanese Patent Application Laid-Open No. Showa 57(1982)-165429, a coating process using an aqueous composition which contains a dispersion containing colloidal silica in a solution prepared by dissolving a partial condensate of a silanol into a mixture of an aliphatic alcohol and water, a buffered latent catalyst for silanol condensation and a xcex2-hydroxyketone compound is proposed as a process for forming a coating layer which is cured in a short time and provides fastness and scratch resistance to the surface of plastic base materials. In Japanese Patent Application Laid-Open No. Showa 62(1987)-32157, a coating composition prepared by mixing an organoalkoxysilane, an alcohol or a glycol, colloidal alumina, an acid and a filler insoluble in water is proposed as a coating composition for forming a coating layer exhibiting excellent heat resistance on the surface of metal, cement and glass. In these coating compositions, alcohols are added in a great amount as hydrophilic organic solvents and water is contained in a great amount as the dispersion medium of the sol. Therefore, these coating compositions have a drawback in that the concentrations of solid substances is small and, moreover, the rates of hydrolysis and polycondensation are very great and stability in storage is poor.
In Japanese Patent Application Laid-Open No. Showa 63(1988)-117074, a coating composition containing a condensate of an organoalkoxysilane, colloidal silica, water and a hydrophilic organic solvent is proposed as a coating composition which exhibits excellent storage stability and forms a coating layer having a high hardness and exhibiting excellent physical properties on the surface of metal, ceramics and glass. This coating composition has a drawback in that the composition tends to cause condensation of water on the surface due to a decrease in the temperature by vaporization of the hydrophilic organic solvent during spray coating. Aggregation of fine silica particles takes place due to the condensation of water and it is difficult that a uniform coating layer is obtained. In Japanese Patent Application Laid-Open No. Heisei 4 (1992)-175388, a coating composition containing, as the essential components, a solution of an oligomer of an organosilane in which silica is dispersed, a polyorganosiloxane having silanol group in the molecule and a catalyst is proposed as a coating composition which is applied to the surface of metal, concrete and plastic base materials, can be cured at a low temperature and can form a coating layer having a high hardness and exhibiting excellent heat resistance and weatherability. This coating composition has a drawback in that the pot life is short after a curing catalyst is added.
In Japanese Patent Application Laid-Open No. Heisei 3 (1991)-31380, a coating composition containing 30 to 90% by weight of a colloidal silica which has the surface modified with an alkoxysilane compound having 2 or more alkoxyl groups and 70 to 10% by weight of a condensate of an organotrialkoxysilane is proposed as a silicone coating composition which forms a thick coating layer having a high hardness and exhibiting excellent heat resistance, wear resistance, chemical resistance, weatherability and gloss on the surface of metal, ceramics, glass and cement and can be stored for a long time. This coating composition has a drawback in that, since water is added in combination with the alkoxysilane and/or condensates having low molecular weights thereof when the surface of the colloidal silica in this coating composition is modified, hydrolysis and polycondensation of the alkoxysilane and/or the condensates having low molecular weights thereof are promoted in the solution and the efficiency of modification of the surface of the colloidal silica decreases. Moreover, since this coating composition does not contain curing catalysts, it takes a long time before the formed coating film is dried sufficiently so that the coating layer can be touched by hands and, therefore, handling of the coated article is difficult.
The present invention has an object of providing a coating composition which exhibits excellent storage stability after addition of a curing agent, suppresses aggregation of fine silica particles during spray coating and forms a coating layer having a high hardness and exhibiting excellent weatherability, water resistance, chemical resistance and adhesion.
As the result of intensive studies by the present inventors to overcome the above drawbacks, it was found that a coating composition comprising a dispersion in an alcohol of fine silica particles which had the hydrophobic surface modified with a hydrocarbon group, a solution comprising a silicone oligomer which was obtained by the reaction of an alkoxysilane with water and a curing agent had a long pot life after addition of the curing agent, suppressed aggregation of fine silica particles during spray coating and formed a coating layer exhibiting excellent physical properties. The present invention has been completed base on this knowledge.
The present invention provides:
(1) A coating composition which comprises:
(A) an alcohol dispersion which comprises silica having a hydrophobic surface and dispersed in an alcohol dispersion medium and has a content of silica in a solid substance of 80% by weight or more;
(B) a solution comprising a silicone oligomer which is obtained by a reaction of an alkoxysilane with water and has an average structural unit represented by:
R1nSiOx/2(OH)y(OR2)z
wherein R1 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality of R1 may represent a same group or different groups when the plurality of R1 are present, R2 represents an alkyl group having 1 to 3 carbon atoms, a plurality of R2 may represent a same group or different groups when the plurality of R2 are present and n, x, y and z represent numbers satisfying relations of: 0.8xe2x89xa6nxe2x89xa61.7, 2 less than x less than 3.2, y greater than 0, z greater than 0 and y+z=4xe2x88x92nxe2x88x92x; and
(C) a curing agent;
(2) A coating composition described in (1), wherein a content of component (A) is 10 to 70% by weight as a solid substance and a content of component (B) is 90 to 30% by weight as a solid substance each based on a total amount of component (A) and component (B) as solid substances and a content of component (C) is 1 to 40 parts by weight per 100 parts by weight of a total amount of component (A) and component (B) as solid substances;
(3) A coating composition described in (1), wherein the silica having a hydrophobic surface in component (A) is obtained by a reaction of fine silica particles with an organoalkoxysilane or an organohalosilane each having a structure represented by:
R3mSiX4xe2x88x92m
wherein R3 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, m represents 1, 2 or 3, a plurality of R3 may represent a same group or different groups when m represents 2 or 3 and X represents Cl, OCH3 or OC2H5;
(4) A coating composition described in (1), wherein the silica having a hydrophobic surface in component (A) is obtained by a reaction, in a presence of an amine-based silane coupling agent, of fine silica particles with an organoalkoxysilane having a structure represented by:
R3mSiX4xe2x88x92m
wherein R3 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, m represents 1, 2 or 3, a plurality of R3 may represent a same group or different groups when m represents 2 or 3 and X represents OCH3 or OC2H5;
(5) A coating composition described in (1), wherein the silicone oligomer in component (B) is prepared by using a metal chelate compound as a catalyst;
(6) A coating composition described in (5), wherein a ligand of the metal chelate compound is at least one compound selected from xcex2-diketones and cyclic polyethers having a large ring;
(7) A coating composition described in (1), wherein the silicone oligomer in component (B) is prepared by using, as a self catalyst, a solution comprising a silicon compound which is soluble in a hydrophilic organic solvent and has an average structural unit represented by:
R4aSiOb/2(OH)C(OR5)d
wherein R4 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality of R4 may represent a same group or different groups when the plurality of R4 are present, R5 represents an alkyl group having 1 to 3 carbon atoms, a plurality of R5 may represent a same group or different groups when the plurality of R5 are present and a, b, c and d represent numbers satisfying relations of: 0xe2x89xa6a less than 3, 0 less than b less than 4, c greater than 0, dxe2x89xa70 and c+d=4xe2x88x92axe2x88x92b;
(8) A coating composition described in (1), wherein component (C) is a solution comprising a complex having a structure represented by:
M(Che)p(OR6)q
wherein M represents a metal having a valence of 3 or greater, Che represents a chelating agent, R6 represents an alkyl group having 1 to 4 carbon atoms, p represents a number of 1 or greater and q represents a number of 2 or greater; or a polynuclear complex comprising said complex as a basic unit;
(9) A coating composition described in (8), wherein the chelating agent is a xcex2-diketone; and
(10) A coating composition described in (1), wherein component (C) comprises a compound which is selected from carboxylic acids, alcohols having carbonyl group and alcohols having ether group and has a boiling point of 200xc2x0 C. or lower.
The coating composition of the present invention comprises (A) an alcohol dispersion which comprises silica having the hydrophobic surface and dispersed in an alcohol dispersion medium and has a content of silica in the solid substance of 80% by weight or more, (B) a solution comprising a silicone oligomer which is obtained by the reaction of an alkoxysilane with water and has an average structural unit represented by: R1nSiOx/2(OH)y(OR2)z and (C) a curing agent. In the above structural formula, R1 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality of R1 may represent the same group or different groups when the plurality of R1 are present, R2 represents an alkyl group having 1 to 3 carbon atoms, a plurality of R2 may represent the same group or different groups when the plurality of R2 are present and n, x, y and z represent numbers satisfying relations of: 0.8xe2x89xa6nxe2x89xa61.7, 2 less than x less than 3.2, y greater than 0, z greater than 0 and y+z=4xe2x88x92nxe2x88x92x. The average structural unit means a structural unit of a silicone oligomer averaged and expressed based on one Si atom.
In the present invention, the silica having the hydrophobic surface is silica in the form of fine particles which have the surface covered with an aliphatic, alicyclic or aromatic hydrocarbon group and exhibits a decreased affinity with water. In the composition of the present invention, the process for producing the alcohol dispersion which comprises silica having the hydrophobic surface and used as component (A) is not particularly limited. For example, the alcohol dispersion which comprises silica having the hydrophobic surface of the fine silica particles can be formed by adding an organoalkoxysilane or an organohalosilane to an alcohol sol containing fine silica particles dispersed in an alcohol dispersion medium, reacting the organoalkoxysilane or the organohalosilane with water adsorbed on the fine silica particles and covering the surface of the fine silica particles with a hydrocarbon group to form the hydrophobic surface. Alternatively, the alcohol dispersion which comprises silica having the hydrophobic surface may be formed by covering the surface of the fine silica particles with a hydrocarbon group by reacting an organoalkoxysilane or an organohalosilane with the fine silica particles and, then, the obtained fine silica particles having the hydrophobic surface may be dispersed in an alcohol dispersion medium. It is preferable that the fine silica particles has diameters of 0.5 xcexcm or smaller. The alcohol used as the dispersion medium is not particularly limited. Alcohols having a low boiling point such as methanol, ethanol, n-propanol and isopropanol are preferable since these alcohols vaporize easily during the coating operation.
Fine particles of other oxides such as alumina, titania and zirconia may be used in place of fine particles of silica. Alcohol dispersions containing the fine particles of these oxides which have the hydrophobic surface formed by the reaction with an organoalkoxysilane or an organohalosilane may be used as component (A). From the standpoint of transparency of the coating film, fine silica particles are preferable as the fine particles of oxides since the fine particles of silica have a refractive index closest to that of the organopolysiloxane which has a low refractive index.
As the alcohol sol in which fine silica particles are dispersed, a commercially available alcohol sol or a dispersion prepared by dispersing fine silica particles having diameters of 0.5 mm or smaller in an alcohol dispersion medium can be used. When an alcohol sol in which fine silica particles are dispersed is used, the surface of the fine silica particles can be made hydrophobic with a hydrocarbon group by the reaction of an organoalkoxysilane or an organohalosilane with water adsorbed on the surface. It is preferable that the organoalkoxysilane or the organohalosilane used above is a compound having a structure represented by R3mSiX4xe2x88x92m. In the formula, R3 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, m represents 1, 2 or 3, a plurality of R3 may represent the same group or different groups when m represents 2 or 3 and X represents C1, OCH3 or OC2H5. Examples of the organosilane include trialkoxysilanes such as methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTES), vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) and isopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such as dimethyldiethoxysilane (DMDE), diphenyldimethoxysilane (DPhDM) and methylethyldimethoxysilane (MEDM); monoalkoxysilanes such as trimethylmethoxysilane (TMMS); and organochlorosilanes such as methyltrichlorosilane, phenyltrichlorosilane, vinyltrichlorosilane, dimethyldichlorosilane, diphenyldichlorosilane and trimethylchlorosilane. The organosilane can be used singly or in combination of two or more.
When the organoalkoxysilane or the organohalosilane is added to the alcohol sol in which fine silica particles are dispersed in an alcohol medium, it is preferable that the organoalkoxysilane or the organohalosilane is used in an amount which is the same as or more than the total amount of water adsorbed on the surface of the fine silica particles and water contained in the alcohol dispersion medium in a small amount. When the reaction is conducted, it is preferable that care is taken as much as possible not to have water mixed into the dispersion medium. When water is present in the dispersion medium in an excess amount, hydrolysis and polycondensation of the organoalkoxysilane or the organohalosilane is promoted and the effect of forming the hydrophobic surface on the fine silica particles is adversely affected. It is preferable that an amine-based silane coupling agent is added to component (A) in an amount of 0.1% by weight or less so that the reaction for forming the hydrophobic surface on the fine silica particles is promoted. The amine-based silane coupling agent used above is not particularly limited. Examples of the silane coupling agent include N-xcex2-aminoethyl-xcex3-aminopropyltrimethoxysilane, N-xcex2-aminoethyl-xcex3-aminopropylmethyl-dimethoxysilane and xcex3-aminopropyltriethoxysilane. When the amine-based silane coupling agent is added, it is preferable that an organoalkoxysilane is used as the agent for forming the hydrophobic surface on the fine silica particles.
In the composition of the present invention, the content of silica in the solid substance is 80% by weight or more and preferably 85% or more in component (A). The silica in the solid substance means silica contained in the alcohol sol before the organoalkoxysilane or the organohalosilane is added. Silicon atoms bonded to the hydrocarbon group which are derived from the organoalkoxysilane or the organohalosilane are not include in the silica in the solid substance. When the amount of silica in the solid substance is less than 80% by weight, the relative amount of the hydrophobic layer on the surface of the fine silica particles increases. As the result, unreacted alkoxyl groups and chlorine are left remaining in a great amount and there is the possibility that the quality of the coating layer is adversely affected.
In the composition of the present invention, the fine silica particles can be incorporated uniformly into the coating layer composed of an organopolysiloxane due to the hydrophobic surface of the fine silica particles and a coating film having a high hardness and a great mechanical strength and exhibiting excellent chemical durability can be obtained.
Component (B) used in the present invention is a solution comprising a silicone oligomer which is obtained by a reaction of an alkoxysilane with water and has an average structural unit represented by R1nSiOx/2(OH)y(OR2)z. In the formula, R1 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality of R1 may represent the same group or different groups when the plurality of R1 are present, R2 represents an alkyl group having 1 to 3 carbon atoms, a plurality of R2 may represent the same group or different groups when the plurality of R2 are present and n, x, y and z represent numbers satisfying relations of: 0.8xe2x89xa6nxe2x89xa61.7 and preferably 1xe2x89xa6nxe2x89xa61.3, 2 less than x less than 3.2 and preferably 2 less than x less than 3, y greater than 0, z greater than 0 and y+z=4xe2x88x92nxe2x88x92x. When the number represented by n is smaller than 0.8, it is difficult that stress is relaxed during drying the coating film and there is the possibility that cracks are formed in the coating film. When the number represented by n exceeds 1.7, the formation of a three-dimensional network structure tends to be difficult and there is the possibility that mechanical properties of the coating film deteriorates. When the number represented by x is smaller than 2, the formation of a linear polymer tends to be difficult and there is the possibility that the amount of volatile component increases. When the number represented by x exceeds 3.2, the relaxation of stress during drying the coating film tends to be difficult and there is the possibility that cracks are formed in the coating film. Since hydroxyl group in the silicone oligomer becomes the crosslinking points in the crosslinking by the action of the curing agent, the presence of hydroxyl group is essential. The presence of the alkoxyl group represented by OR2 is essential for maintaining the storage stability of the solution before the addition of the curing agent.
The alkoxysilane used for the preparation of component (B) is not particularly limited. Examples of the alkoxysilane include tetraalkoxysilanes such as tetramethoxysilane (TMOS) and tetraethoxy-silane (TEOS); trialkoxysilanes such as methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTES), vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) and isopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such as dimethyldiethoxysilane (DMDE), diphenyldimethoxysilane (DPhDM) and methylethyldimethoxysilane (MEDM); and monoalkoxysilanes such as trimethylmethoxysilane (TMMS).
In the preparation of component (B) used in the present invention, it is preferable that water and the alkoxysilane are mixed in amounts such that the ratio of the amount by mole of H2O to the amount by mole of Si is in the range of 1.4 to 4.0 and more preferably in the range of 1.4 to 2.5 and the hydrolysis and the polycondensation are conducted. When the ratio of the amount by mole of H2O to the amount by mole of Si is smaller than 1.4, there is the possibility that the unreacted alkoxyl group is left remaining in a great amount and the amount of the oligomer having high molecular weights decreases. Therefore, there is the possibility that mechanical property of the coating film are adversely affected. When the ratio of the amount by mole of H2O to the amount by mole of Si exceeds 4.0, water tends to be condensed on the surface during the spray coating and there is the possibility that formation of a uniform coating film becomes difficult during the film formation. When the ratio of the amount by mole of H2O to the amount by mole of Si is adjusted within the range of 1.4 to 4.0, a portion of the alkoxyl group remains and the effect of improving the stability of the solution containing the silicon oligomer of component (B) is exhibited.
In the preparation of component (B) of the composition of the present invention, it is preferable that an acid catalyst conventionally used for the sol-gel reaction is not used as the catalyst for the hydrolysis but, instead, a metal chelate compound is used as the catalyst for the hydrolysis. When the acid catalyst is used, there is the possibility that gel tends to be formed. The metal chelate compound used as the catalyst for the hydrolysis exhibits not only the catalytic effect on the hydrolysis of alkoxide but also the effect of suppressing crystallization when a methyltrialkoxysilane is used in a great amount as the raw material. Moreover, the metal chelate compound exhibits the effect of promoting linear propagation of the polycondensation by deprotonation of the silanol in addition to the catalytic effect on the hydrolysis. Therefore, the obtained liquid has excellent storage stability for a long time and the use of the metal chelate compound is advantageous for the formation of a coating film. The metal chelate compound is not particularly limited. Metal chelate compounds having xcex2-diketones or cyclic polyethers having a large ring as the ligands can be preferably used. The type of the metal ion is not particularly limited. Metal ions having a great constant of complex formation with the ligand are preferably used.
Examples of the metal chelate compound include metal chelate compounds of xcex2-diketones such as tris(acetylacetonato)aluminum(III), tris(ethyl acetoacetato) aluminum(III), tris(diethyl malonato)aluminum(III) bis(acetylacetonato)copper(II), tetrakis(acetylacetonato)zirconium-(IV), tris(acetylacetonato)chromium(III), tris(acetylacetonato)cobalt(III) and titanium(II) oxyacetylacetonate [(CH3COCHCOCH3)2TiO]; metal chelate compounds of xcex2-diketones with rare earth metals; and metal chelate compounds of cyclic polyethers having a large ring such as 18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelate compound salts and 15-crown-5-sodium chelate compound salts.
The amount of the metal chelate compound is not particularly limited and can be suitably selected in accordance with the catalytic effect. In general, it is preferable that the amount is 0.001 to 5% by mole and more preferably 0.005 to 1% by mole based on the amount of the alkoxysilane. When the amount of the metal chelate compound is less than 0.001% by mole based on the amount of the alkoxysilane, there is the possibility that the catalytic effect on the hydrolysis is not exhibited sufficiently. When the amount of the metal chelate compound exceeds 5% by mole based on the amount of the alkoxysilane, there is the possibility that the metal chelate compound is precipitated during the formation of a coating film and the properties of the coating film are adversely affected. When a self-catalyst is used, the amount of the metal chelate compound include the amount of the metal chelate compound derived from the self-catalyst.
In the preparation of component (B) of the composition of the present invention, the alkoxysilane may be hydrolyzed and polycondensed by using a solution comprising a silicon compound which has an average structural unit represented by R4aSiOb/2(OH)c(OR5)d and is soluble in a hydrophilic organic solvent as a self catalyst. In the formula, R4 represents an alkyl group having 1 to 3 carbon atoms, phenyl group or vinyl group, a plurality of R4 may represent the same group or different groups when the plurality of R4 are present, R5 represents an alkyl group having 1 to 3 carbon atoms, a plurality of R5 may represent the same group or different groups when the plurality of R5 are present and a, b, c and d represent numbers satisfying relations of: 0xe2x89xa6a less than 3 and preferably 0.8xe2x89xa6a less than 2, 0 less than b less than 4 and preferably 1 less than b less than 3, c greater than 0, d less than 0 and c+d=4 less than a less than b. The average structural unit means a structural unit of a silicon compound averaged and expressed based on one Si atom. When the number represented by a exceeds 3, the above silicon compound tend to be vaporized and there is the possibility that the silicon compound is condensed and deactivated. When the number represented by c is greater than 0 and the silanol group is present, the hydrolysis of the alkoxysilane with water is promoted and polycondensation is also promoted due to protonation of the alkoxysilane with proton in the silanol. The silicone oligomer itself in the solution of a silicon oligomer which is the product of the hydrolysis and the polycondensation of the alkoxysilane can be the above silicon compound having the above average structural unit represented by R4aSiOb/2(OH)c(OR5)d which is used as the catalyst for the reaction. Therefore, this type of the catalyst is defines as a self-catalyst. It is preferable that the added amount of the self-catalyst is in the range of 0.1 to 50% by weight and more preferably in the range of 1 to 40% by weight based on the amount of the alkoxysilane. When the added amount of the self-catalyst is less than 0.1% by weight based on the amount of the alkoxysilane, the amount of transfer of proton is small and there is the possibility that the efficiency of the hydrolysis decreases. When the added amount of the self-catalyst exceeds 50% by weight based on the amount of the alkoxysilane, the amount of the silicone oligomer derived from the catalyst increases in the solution of the silicone oligomer obtained by the reaction and there is the possibility that the efficiency of production of the silicone oligomer decreases. Moreover, there is the possibility that the quality of the obtained solution of the silicone oligomer becomes unstable.
When the solution of the self-catalyst is prepared from the alkoxysilane, it is preferable that at least one compound selected from acids and metal chelate compounds is added as the catalyst. As the acid, an acid conventionally used in the sol-gel reaction, for example, an a inorganic acid such as nitric acid and hydrochloric acid and an organic acid such as acetic acid, can be used. When a coating film is formed on the surface of a metal base material, it is preferable that a catalyst of a metal chelate compound is used so that corrosion at the interface is suppressed. When a great amount of the self-catalyst is added in the preparation of the solution of the silicone oligomer of the present invention, it is preferable that a catalyst of a metal chelate compound is used since there is the possibility that the use of an acid catalyst causes deterioration in the storage stability.
A fresh solution of the self-catalyst can be prepared by hydrolysis and polycondensation of an alkoxysilane using the solution of the self-catalyst thus obtained as the catalyst. In this case, it is preferable that a catalyst of a metal chelate compound is used in combination.
The alkoxysilane used for the preparation of the solution of a self-catalyst is not particularly limited. Examples of the alkoxysilane include tetraalkoxysilanes such as tetramethoxy-silane (TMOS) and tetraethoxysilane (TEOS); trialkoxysilanes such as methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS), phenyl-triethoxysilane (PhTES), vinyltriethoxysilane (VTES), n-propyl-trimethoxysilane (n-PrTMS) and isopropyltrimethoxysilane (iso-PrTMS); dialkoxysilanes such as dimethyldiethoxysilane (DMDE), diphenyl-dimethoxysilane (DPhDM) and methylethyldimethoxysilane (MEDM); and monoalkoxysilanes such as trimethylmethoxysilane (TMMS).
The catalyst of a metal chelate compound used for preparation of the solution of a self-catalyst is not particularly limited. Metal chelate compounds having xcex2-diketones and cyclic polyethers having a large ring can be preferably used. The type of the metal ion is not particularly limited. Metal ions having a great constant of complex formation with the ligand can be preferably used. Examples of the metal chelate compound include metal chelate compounds of xcex2-diketones such as tris(acetylacetonato)aluminum(III), tris(ethyl acetoacetato)aluminum(III), tris(diethyl malonato)aluminum(III), bis(acetylacetonato)copper(II), tetrakis(acetylacetonato)zirconium(IV), tris(acetylacetonato)chromium(III), tris (acetylacetonato)cobalt(III) and titanium (II) oxyacetylacetonate [(CH3COCHCOCH3)2TiO]; metal chelate compounds of xcexc-diketones with rare earth metals; and metal chelate compounds of cyclic polyethers having a large ring such as 18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelate compound salts and 15-crown-5-sodium chelate compound salts.
The amount of the catalyst of the metal chelate compound added in the preparation of the solution of the self-catalyst is not particularly limited and can be suitably selected in accordance with the catalytic effect. In general, it is preferable that the amount is 0.001% by mole or more and more preferably 0.005% by mole or more based on the amount of the alkoxysilane. When the amount of the metal chelate compound is less than 0.001% by mole based on the amount of the alkoxysilane, there is the possibility that the catalytic effect on the hydrolysis is not exhibited sufficiently. There is no upper limit in the amount of the catalyst of the metal chelate compound based on the amount of the alkoxysilane as long as the metal chelate compound is homogeneously dissolved.
In the composition of the present invention, a major portion of the solvent of the solution comprising the silicone oligomer of component (B) is the alcohol formed by the hydrolysis of the alkoxysilane. Preparation of the solution of the silicone oligomer which is stable and has a high concentration of solid substances is made possible by utilizing the alcohol formed by the hydrolysis without adding other solvents. In the composition of the present invention, the molecular weight of the silicone oligomer is not particularly limited. A silicone oligomer having a high molecular weight can be used as long as the silicone oligomer formed by hydrolysis and polycondensation of the alkoxysilane is dissolved into the alcohol formed simultaneously and a homogeneous solution is formed.
In the composition of the present invention, it is preferable that the curing agent used as component (C) is a solution comprising a complex having the structure represented by M(Che)p(OR6)q or a polynuclear complex comprising the above complex as a basic unit. In the above formula, M represents a metal having a valence of 3 or greater, Che represents a chelating agent, R6 represents an alkyl group having 1 to 4 carbon atoms, p represents a number of 1 or greater and q represents a number of 2 or greater. In the composition of the present invention, the curing agent of component (C) is added to a mixture of component (A) and component (B) before the coating composition is used for the coating and exhibits the effect of promoting crosslinking in the process of formation of the coating film. The metal ion having a valence of 3 or greater which is represented by M is not particularly limited. Examples of the metal ion having a valence of 3 or greater include Al3+, Ti4+and Zr4+. Examples of the reactive functional group represented by OR6 include methoxyl group, ethoxyl group, n-propoxyl group, isopropoxyl group, n-butoxyl group, secbutoxyl group and tert-butoxyl group. When the number represented by q is 2 or greater, i.e., when the number of the reactive group represented by OR6 is 2 or greater, the curing agent exhibits the effect of promoting the crosslinking and a further effect of forming the crosslinking with the reactive group itself. The chelating agent represented by Che is not particularly limited. Examples of the chelating agent include acetylacetone, ethyl acetoacetate and diethyl malonate.
In the composition of the present invention, it is preferable that the curing agent of component (C) comprises a compound which is selected from carboxylic acids, alcohols having carbonyl group and alcohols having ether group and has a boiling point of 200xc2x0 C. or lower and preferably 170xc2x0 C. or lower. Examples of the above compound include carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, acrylic acid, isocrotonic acid and methacrylic acid; xcex2-hydroxyketone compounds such as diacetone alcohol; alcohols having carbonyl group such as ethylene glycol monoacetate; alcohols having ether group such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-(methoxymethoxy)ethanol, ethylene glycol monoisopropyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether. The above compound can be used singly or in combination of two or more.
When the curing agent comprises a carboxylic acid, an alcohol having carbonyl group or an alcohol having ether group, this compound acts as a stabilizer and the pot life of the coating composition comprising component (A), component (B) and component (C) increases to facilitate handling. This compound exchanges the ligand with the group represented by OR6 in the compound represented by M(Che)p(OR6)q which is the component of the curing agent. The stability of the curing agent is improved by forming a partially chelated metal complex and, as the result, the stability of the coating composition is improved. On the other hand, after the coating composition is applied and a coating film is formed, the compound with which the ligand has been exchanged is removed and the effect of promoting curing after the formation of the coating film does not decrease. In this manner, a uniform coating film having excellent mechanical properties can be obtained. It is preferable that this compound is added in an amount of 0.5 moles or more per 1 mole of the metal represented by M. It is preferable that the curing is conducted at a temperature in the range of the room temperature to 200xc2x0 C.
In the coating composition of the present invention, it is preferable that the content of component (A) is 10 to 70% by weight as a solid substance and the content of component (B) is 90 to 30% by weight as a solid substance each based on the total amount of component (A) and component (B) as solid substances. When the content of component (A) as a solid substance is smaller than 10% by weight or the content of component (B) as a solid substance exceeds 90% by weight based on the total amount of component (A) and component (B), there is the possibility that hardness and mechanical strength of the coating film decrease. When the content of component (A) as a solid substance exceeds 70% by weight or the content of component (B) as a solid substance is smaller than 30% by weight based on the total amount of component (A) and component (B), there is the possibility that the coating film becomes fragile due to the excessively small content of the organopolysiloxane as the binder of the fine silica particles. It is more preferable that the content of component (A) is 15 to 60% by weight as a solid substance and the content of component (B) is 85 to 40% by weight as a solid substance each based on the total amount of component (A) and component (B) as solid substances.
In the coating composition of the present invention, it is preferable that the content of component (C) is 1 to 40 parts by weight per 100 parts by weight of the total amount of component (A) and component (B) as solid substances. When the content of component (C) is smaller than 1 part by weight per 100 parts by weight of the total amount of component (A) and component (B) as solid substances, there is the possibility that curing after the coating becomes insufficient. When the content of component (C) exceeds 40 part by weight per 100 parts by weight of the total amount of component (A) and component (B) as solid substances, there is the possibility that the pot life of the coating composition obtained by mixing component (A), component (B) and component (C) is short and there is the possibility that problems arise in the operation. It is more preferable that the content of component (C) is 2 to 25 parts by weight per 100 parts by weight of the total amount of component (A) and component (B) as solid substances.
The process for application of the coating composition of the present invention is not particularly limited and any conventional coating process can be selected in accordance with the shape of the coated article and the object of the coating. For example, any of the spray coating process, the dipping coating process, the flow coating process and the roll coating process can be selected. The thickness of the coating film can be selected in accordance with the object of coating. In general, it is preferable that the thickness is in the range of 1 to 50 xcexcm.
The coating composition of the present invention is applied to inorganic base materials such as metal, glass, ceramics and concrete and organic base materials such as acrylic resins, ABS resins, wood and paper to protect the surface of the base materials and enhance the excellent appearance.